In the industrial production of components, during surface machining damage may occur. Particularly in the mass production of components it is therefore necessary by means of a suitable inspection method to recognize such damage so that the damaged components can be separated out and the production process modified so as to avoid it.
A frequently occurring form of surface damage is the so-termed grinding burn, which for example can take place during tooth grinding to produce the final contour of toothed components. For the recognition of surface damage or grinding burn, from the prior art chemical etching methods are known. During so-termed Nital etching the component to be inspected is treated with various acids and electrolytes such that after the treatment, surface damage and particularly grinding burn can be recognized by virtue of color changes on the component. Nital etching is on the one hand not environmentally friendly, and on the other hand it incurs very high costs for the maintenance and disposal of the acids and electrolytes used. Furthermore, it is a subjective inspection method in which the surface damage is assessed by human experts by virtue of the discoloration. Thus, Nital etching is not suitable for inspecting the surface of components in the context of mass production.
From the prior art the so-termed Barkhausen Noise Analysis is also known, with which the surface of ferromagnetic materials can be inspected by means of appropriate sensors. In the documents EP 0 100 009 A1 and DE 43 33 830 A1 methods for surface analysis taking account of Barkhausen noises are described. Barkhausen Noise Analysis is based on the so-termed Barkhausen jumps, which are produced by the reversal of magnetization in ferromagnetic materials in a magnetic field of slowly increasing strength. Ferromagnetic materials consist of small magnetic regions (called domains) with a uniform magnetization direction. The domains are separated from one another by Bloch walls, within which the magnetization direction changes through the width of the walls. A movement of the Bloch walls can be brought about by an external magnetic field. If at the same time a coil is positioned close to the ferromagnetic component, the magnetization produces an electric pulse in the coil. Addition of the impulses produces a noise-like signal, also known as Barkhausen noise or a Barkhausen noise signal. The Barkhausen noise signal depends on the surface condition and in particular on the surface hardness. By means of the Barkhausen noise signal grinding burn can be detected, since grinding burn reduces the surface hardness.
Even though by way of Barkhausen noise analysis surface damage can be recognized, the present analysis methods do not provide any conclusions about the causes, during the production process of the component, that have resulted in the surface damage. Accordingly, it is desirable to extend Barkhausen noise analysis in such manner that the causes of surface damage are recognized.